Reinforcement of extended polymers has recently become a problem of great importance due to an increasing demand for high-strength polymeric materials. The use of reinforcing fillers (such as glass fiber, mineral fiber, metals, metal oxides and the like) improves properties of polymers. An essential property of high mechanical strength extended polymers is sufficient adhesion between a filler and a polymer. To ensure higher adhesion various substances are used which are referred to as sizing agents.
Sizing agents are monomeric bifunctional compounds capable of interaction both with a mineral filler and a polymer. Fillers (extenders) are treated with sizing agents either by application of the latter onto the filler surface or by treating fillers with the sizing agent vapors, or by mixing with a powder-like sizing agent.
After such treatment the filler is incorporated into a polymer. Besides, a sizing agent may be directly introduced into a polymer, wherein it migrates to the surface of a filler during the mixing process. Thus-extended polymers have improved mechanical properties, increased aging-resistance under severe conditions. (cf. G. D. Andrievskaja "High-strength oriented glass plastics", M., "Nauka" Publishing House; coll. of rev. and transl. from foreign periodicals, Moscow, MIR Publishing House, 1968; Express-information "Synthetic polymer materials", No. 36, 38, 1976).
Known in the art is a process for producing mineral fillers containing graft unsaturated or saturated groups or other reactive groups and intended for polymers such as polystyrene, polyethylene, polypropylene which comprises treatment of said fillers, at a temperature within the range of from 50.degree. to 150.degree. C., with sizing agents, i.e. silicone compounds of the formula: EQU R.sub.4-y SiX.sub.y,
wherein R is an organic functional group capable of reacting with a polymer; X is a halogen, an alkoxy or acyloxy group; y=1, 2, 3; followed by separation and drying of the treated mineral filler (cf. Reviews in Polymer Technology, Ed. by J. S. Keit, Vol. 1, No. 4, 1972, p. 1-49).
However, to produce extended polymers with satisfying physico-mechanical properties, it is necessary to select sizing agents containing specific groups R and X defined by the type of filler and polymer. Furthermore, the compounds employed as sizing agents cannot be used, due to the structure thereof, for a simultaneous combination of two polymers having different natures.
Known in the art is a process for producing mineral fillers containing graft peroxy groups and intended for polyethylene, polysulphones which comprises treatment of said fillers with a sizing agent of the formula: CH.sub.2 .dbd.CHSi [OOC(CH.sub.3).sub.3 ] which is an organosilicon peroxide. This sizing agent is applied to a mineral filler which is then compounded with a polymer at a temperature within the range of from 175.degree. to 230.degree. C. As a result, upon heating, the peroxide forms free radicals serving as initiators for grafting the polymer onto the filler (cf. Mod. Plast. Intern., 6, No. 6, 28, 31, 1976).
This prior art process has a disadvantage residing in a limited field of application of such sizing agents due to a high temperature of decomposition of the organosilicon peroxide. This sizing agent is readily hydrolyzed by the air humidity and necessitates specific storage conditions. Furthermore, synthesis of this sizing agent is a quite complicated and expensive process.